package com.summli.basic.class03;

/**
 *
 * 在一个数组中，一个数左边比它小的数的总和，叫数的小和，所有数的小和累加起来，叫数组小和。求数组小和。
 * 例子： [1,3,4,2,5]
 * 1左边比1小的数：没有
 * 3左边比3小的数：1
 * 4左边比4小的数：1、3
 * 2左边比2小的数：1
 * 5左边比5小的数：1、3、4、 2
 * 所以数组的小和为1+1+3+1+1+3+4+2=16
 *
 */
public class Code02_SmallSum {
    private static int smallSum(int[] arr){
        if(arr == null || arr.length<2){
            return 0;
        }
        return process(arr,0,arr.length-1);
    }

    private static int process(int[] arr, int l, int r) {
        if(l == r){
            return 0;
        }
        int m = l+((r-l)>>1);
        int result1 =process(arr, l, m);
        int result2 =process(arr,m+1,r);
        int result3 =merge(arr,l,m,r);
        return result1+result2+result3;
    }

    private static int merge(int[] arr, int l, int m, int r) {
        int[] help = new int[r-l+1];
        int minSum = 0;
        int i=0;
        int p1 = l;
        int p2 = m+1;
        while(p1<=m && p2 <=r){
            if(arr[p1]<arr[p2]){
                minSum += arr[p1]*(r-p2+1);
                help[i++] = arr[p1++];
            }else{
                help[i++] = arr[p2++];
            }
        }
        while(p1<=m){
            help[i++] = arr[p1++];
        }
        while(p2<=r){
            help[i++] = arr[p2++];
        }
        for (i = 0; i < help.length; i++) {
            arr[l+i] = help[i];
        }
        return minSum;
    }
    // for test
    public static int comparator(int[] arr) {
        if (arr == null || arr.length < 2) {
            return 0;
        }
        int res = 0;
        for (int i = 1; i < arr.length; i++) {
            for (int j = 0; j < i; j++) {
                res += arr[j] < arr[i] ? arr[j] : 0;
            }
        }
        return res;
    }

    // for test
    public static int[] generateRandomArray(int maxSize, int maxValue) {
        int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
        }
        return arr;
    }

    // for test
    public static int[] copyArray(int[] arr) {
        if (arr == null) {
            return null;
        }
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    // for test
    public static boolean isEqual(int[] arr1, int[] arr2) {
        if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
            return false;
        }
        if (arr1 == null && arr2 == null) {
            return true;
        }
        if (arr1.length != arr2.length) {
            return false;
        }
        for (int i = 0; i < arr1.length; i++) {
            if (arr1[i] != arr2[i]) {
                return false;
            }
        }
        return true;
    }

    // for test
    public static void printArray(int[] arr) {
        if (arr == null) {
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    // for test
    public static void main(String[] args) {
        int testTime = 500000;
        int maxSize = 100;
        int maxValue = 100;
        boolean succeed = true;
        for (int i = 0; i < testTime; i++) {
            int[] arr1 = generateRandomArray(maxSize, maxValue);
            int[] arr2 = copyArray(arr1);
            if (smallSum(arr1) != comparator(arr2)) {
                succeed = false;
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println(succeed ? "Nice!" : "Fucking fucked!");
    }

    /*public static void main(String[] args) {
        int[] arr = {1,2,3};
        System.out.println(smallSum(arr));
    }*/
}
